Over the years various surgical instruments for joining tissue have been developed. Most instruments have been developed utilizing metal staples for joining the tissue. The metal staples are relatively rigid, have their legs sharpened to readily penetrate the tissue, and once penetrated may then be crimped into a clinched position to hold the tissue together as is well known in the art. Instruments of this type are more fully disclosed and described in U.S. Pat. Nos. 3,080,564, 3,079,606, 2,891,250, 3,589,589, 4,207,898 and 4,351,466.
Generally, the instruments comprise a movable member or jaw and a stationary member or jaw. The movable jaw usually carries the metal staples and the stationary jaw carries an anvil which clinches or bends the legs of the staple that pass through the tissue. In use, the tissue is placed between the jaws, the jaws brought to the appropriate gap and the staples driven through the tissue and clinched to set the staple. A major problem with these instruments is the use of the metal staple. While metal staples provide desired hemostatsis in the joining of the tissue, they remain in the tissue and can disrupt future diagnostic techniques such as x-ray diagnosis, computer axial tomography, nuclear magnetic resonance, and the like. To eliminate this problem, it has been found desirable to develop instruments which can set nonmetallic fasteners. These are fasteners made from biologically absorbable or non-absorbable polymeric materials. Examples of such non-absorbable polymeric materials would be the polyolefins, polyesters, and the like. Examples of the absorbable polymeric materials would be the polymers and copolymers of glycolide, lactide, dioxanone, etc. These polymeric materials do not have the dead-bend morphology of a metal and, hence, they cannot be clinched in the same manner as a metal staple. To use these polymers, the fasteners are designed as two-piece fasteners. This means one piece of the fastener is placed on one side of the tissue to be joined and the second piece of the fastener is placed on the other side of the tissue to be joined. One piece of the fastener is a U-shaped staple which has legs which are caused to penetrate the tissue. On the opposite side of the tissue is the second fastener piece or receiver which is a member used to engage the legs to interlock therewith once the legs have penetrated the tissue and, hence, join the tissue together.
As can be appreciated this major change in design and configuration of fasteners causes a number of problems. First, the fasteners must be designed to be sufficiently sharp and strong to penetrate the tissue or in certain instances some aiding means must be used with the fastener to assist in penetrating the tissue. Also, the fasteners must be designed to develop an interlocking between the two pieces.
These differences cause various types of forces to be used when joining the tissue together, and these forces are different from the forces required when joining tissue using metallic fasteners. Also, when utlizing the two-piece fasteners, alignment between the two fasteners is extremely critical. As can be appreciated, when applying these fasteners the instrument must hold the pieces until one piece has penetrated the tissue and the opposite piece is interengaged and locked on to the penetrating portion of the other member. Once this is accomplished the instrument must then release both pieces preferably simultaneously.
Surgical instruments whether reusable or disposable and whether they apply a metal or a plastic fastener should be extremely reliable. They should function with absolute certainty and each instrument should function in the same manner. Such repetitive reliability is required to allow surgeons to adequately develop their surgical techniques and to keep trauma to a minimum during surgical procedures. Along with this desirable total repetitive reliability the instrument should be simple to construct and economical to produce. In surgical instruments for placing fasteners it is important that the instrument not be actuatable to place the fastener until the tissue is in place to be joined and the appropriate gap has been set between the jaws of the instrument.
It is an object of the present invention to provide instruments having identical actions and operations especially in the placement of the fastener once the appropriate gap has been set between the jaws of the instrument. It is also an object of the present invention to provide an instrument which is simple in construction and economical to produce.